CHAP. III. FUNCTION OF NUTRITION. 20? 



descent and general transfusion of the sap, we can 

 trace the operation of physical causes modifying and 

 controlling to a considerable extent, if indeed they do 

 not originate and entirely regulate these movements. 

 We have now to describe a more remarkable movement of 

 the juices of some plants, which more decidedly evinces 

 a vital action. This movement consists in a constant 

 rotation of the fluid contained in their vesicles and tubes, 

 and rendered apparent by the presence of minute glo- 

 bules of vegetable matter floating in it. The original 

 disovery of this phenomenon was made about a century 

 ago by Corti, who first observed it in the Cauliniafra- 

 gilis, a maritime plant found on the shores of Italy. 

 His observations appear to have been generally neg- 

 lected until lately, when the re-discovery of the pheno- 

 menon in other plants has excited the attention of 

 botanists. It may readily be seen with a good lens 

 in Valisneria, Hydrocharis, Potamogeton, and other 

 aquatic genera, but more especially in the genus Chara. 

 It has also been observed in the terrestrial genera Cu- 

 curbita, Cucumis, Pistia, and others ; and is more es- 

 pecially observable in the hairs of many species. It 

 appears to be a universal property of the cellular 

 tissue though it is impossible in many cases to de- 

 tect it, either on account of the want of sufficient 

 transparency in the membrane or from the absence of 

 the granular matter by whose presence alone the ro- 

 tation of the fluid itself can be observed. We shall 

 explain the phenomenon as it may be seen in the 

 Chara with a lens of about the tenth of an inch focal 

 distance or even of less power. 



(194.) Rotation of Fluid in Chara. This genus 

 may be divided into two sections, which are considered 

 as distinct genera by Agardh. In one of them, the 

 true Chara, the stems are composed of a central tube 

 jointed at intervals and surrounded by a row of smaller 

 tubes. In the other section, or genus Nitella, the 

 stems consist of single tubes jointed as before. If we 

 select a species of the first section it will be necessary 



